Multiphysics Design and Sensitivity Analysis of Nuclear Heated Critical Heat Flux Pool Boiling Test Devices in TREAT.

Following the events of the 2011 Fukushima Daiichi accident, there has been a drive to develop accident tolerant fuels (ATF) capable of enhancing safety margins provided by conventional light water reactor (LWR) materials, with a focus on the critical heat flux (CHF) behavior under fast transient heating irradiation conditions. Presented in this dissertation, is the modeling scope of a current effort aimed at elucidating the mechanisms of CHF under in-pile fast transient irradiation conditions using the Transient Reactor Test (TREAT) facility. A heater rodlet made from stainless steel type-304 with tailored natural boron content was held within experimental pool boiling capsules, to induce CHF in the surrounding coolant when submitted to a power pulse. The experimental aspect of this project is focused on studying the CHF impacts of radiation-induced surface activation (RISA), as well as rapid surface heating effects. The initial unique contributions of the computational studies in this dissertation, depict the multiphysics design process of an experimental separate effects borated heater apparatus that was inserted into TREAT in December of 2019. Boron concentrations between 0.1-2.09 wt.% were considered. A self-shielding study determined that a borated tube could be used instead of a solid rod. Following, a thermal hydraulics study determined that the current borated tube configuration achieved a maximum CHF multiplier value of 7.8 using a 1400 MJ power pulse in TREAT. Following, sensitivity studies analyzed the potential impacts of the CHF event on the heat transfer of more complex integral TREAT experiments under rapid heating conditions, utilizing the heat transfer time constant (HTTC) as the fundamental basis. The analysis showed the maximum fuel centerline temperature is independent of the CHF event, and the UO2 volumetric heat capacity is the only significant HTTC parameter. For the peak outer cladding temperatures (POCTs), the occurrence of DNB was determined to be dominant on the heat transfer mechanisms of these experimental fuel designs. For the cases where the DNB event manifested, the HTTC was resolved to have significant impacts on the predictions of the POCTs. Furthermore, when studying the time occurrence of the CHF, the variations in the gap thickness was dominant

Multi-step Reinforcement Learning: A Unifying Algorithm

Unifying seemingly disparate algorithmic ideas to produce better performing algorithms has been a longstanding goal in reinforcement learning. As a primary example, TD($\lambda$) elegantly unifies one-step TD prediction with Monte Carlo methods through the use of eligibility traces and the trace-decay parameter $\lambda$. Currently, there are a multitude of algorithms that can be used to perform TD control, including Sarsa, $Q$-learning, and Expected Sarsa. These methods are often studied in the one-step case, but they can be extended across multiple time steps to achieve better performance. Each of these algorithms is seemingly distinct, and no one dominates the others for all problems. In this paper, we study a new multi-step action-value algorithm called $Q(\sigma)$ which unifies and generalizes these existing algorithms, while subsuming them as special cases. A new parameter, $\sigma$, is introduced to allow the degree of sampling performed by the algorithm at each step during its backup to be continuously varied, with Sarsa existing at one extreme (full sampling), and Expected Sarsa existing at the other (pure expectation). $Q(\sigma)$ is generally applicable to both on- and off-policy learning, but in this work we focus on experiments in the on-policy case. Our results show that an intermediate value of $\sigma$, which results in a mixture of the existing algorithms, performs better than either extreme. The mixture can also be varied dynamically which can result in even greater performance.Comment: Appeared at the Thirty-Second AAAI Conference on Artificial Intelligence (AAAI-18

Nurturing the talent pipeline for an emerging global workforce

Passion. IMSA’s ability to produce thinkers and problem solvers doesn’t just breed pragmatists who know what it takes to be successful – it also gives students the chance to discover their passion. The more they try and the more they experience, the more they discover what they love. The chance to pursue passion means graduates have a greater sense of vision – and a greater chance of realizing their true potential. IMSA teaches students to be global citizens in a diverse world. IMSA embraces diverse perspectives enriching understanding and the knowledge, attitudes, and skills required to function as multicultural citizens in a global world. The false perception that IMSA is just a school for smart kids might blind people from seeing what truly makes IMSA special. There are plenty of places to be smart – IMSA shares in the responsibility to enable students to be successful in the emerging future of a global workforce

Low Baseline Pneumococcal Antibody Titers Predict Specific Antibody Deficiency, Increased Upper Respiratory Infections, and Allergy Sensitization.

Background:Inadequate titers of pneumococcal antibody (PA) are commonly present among patients with recurrent respiratory infections. Objective:We sought to determine the effect of the degree of inadequacy in baseline PA titers on the subsequent polysaccharide vaccine response, the incidence of sinusitis, and allergic conditions. Methods:A total of 313 patients aged 6 to 70 years with symptoms of recurrent respiratory infections were classified by baseline-pPA (percentage of protective [≥1.3 µg/mL] PA serotypes/total tested serotypes) and postvaccination pPA (post-pPA): Group A (adequate baseline-pPA), Group B (inadequate baseline-pPA, adequate post-pPA, responders), and Group C (inadequate baseline-pPA, inadequate postpPA, nonresponders, specific antibody deficiency [SAD]). Immunity against Streptococcus pneumoniae was defined as adequate when the pPA was ≥70%. Each group and combined groups, Group AB (inadequate baseline-pPA), and Group BC (adequate post-pPA) were analyzed for demographics, history of sinusitis, recurrent sinusitis in the following year, allergic conditions, and association with inadequate individual serotype titers. Results:Over 80% of patients with respiratory symptoms had inadequate baseline-pPA. Baseline-pPA and SAD prevalence are inversely related (odds ratio = 2.02, 95% CI: 1.15-3.57, P = .01). Inadequate serotype 3 antibody titer is highly associated with SAD (odds ratio = 2.02, 96% CI: 1.61-5.45, P < .01). The groups with inadequate pPA (Group B and C, or BC) had significantly higher percentage of patients with chronic rhinosinusitis (P < .001), allergic sensitization, and allergic rhinitis (P < .05). Group A contained higher percentage of patients with recurrent upper airway infections (P < .001). Conclusion:Low baseline-pPA and low antibody titers to serotype 3 are highly associated with SAD, increased incidence of respiratory infections including CRS and allergic conditions

High resolution imaging of NGC 2346 with GSAOI/GeMS: disentangling the planetary nebula molecular structure to understand its origin and evolution

We present high spatial resolution ($\approx$ 60--90 milliarcseconds) images of the molecular hydrogen emission in the Planetary Nebula (PN) NGC 2346. The data were acquired during the System Verification of the Gemini Multi-Conjugate Adaptive Optics System + Gemini South Adaptive Optics Imager. At the distance of NGC 2346, 700 pc, the physical resolution corresponds to $\approx$ 56 AU, which is slightly higher than that an [N II] image of NGC 2346 obtained with HST/WFPC2. With this unprecedented resolution we were able to study in detail the structure of the H$_2$ gas within the nebula for the first time. We found it to be composed of knots and filaments, which at lower resolution had appeared to be a uniform torus of material. We explain how the formation of the clumps and filaments in this PN is consistent with a mechanism in which a central hot bubble of nebular gas surrounding the central star has been depressurized, and the thermal pressure of the photoionized region drives the fragmentation of the swept-up shell.Comment: accepted in ApJ (17 pages, 7 figures, 1 Table

Effects of Hydrogen Bonding and Molecular Chain Flexibility of Substituted n-Alkyldimethylsilanes On Impact Ice Adhesion Shear Strength

The effects of hydrogen bonding and molecular flexibility upon ice adhesion shear strength were investigated using aluminum substrates coated with substituted n-alkyldimethylalkoxysilanes. The location of the chemical group substitution was on the opposing end of the linear n-alkyl chain with respect to silicon. Three hydrogen-bonding characteristics were evaluated: 1) non-hydrogen bonding, 2) donor/acceptor, and 3) acceptor. Varying the length of the n-alkyl chain provided an assessment of molecular chain flexibility. Coated and uncoated aluminum surfaces were characterized by receding water contact angle and surface roughness. Ice adhesion shear strength was determined in the Adverse Environment Rotor Test Stand facility from -16 to -8C that simulated aircraft in-flight icing conditions within the FAR Part 25/29 Appendix C icing envelope. Surface roughness of the coatings was similar allowing for comparison of the test results. An adhesion reduction factor, based on the ice adhesion shear strength data with respect to uncoated aluminum obtained at the same temperature, was calculated to compare the data. The results revealed complex interactions with impacting supercooled water droplets that were interdependent upon ice accretion temperature, surface energy characteristics of water and ice, hydrogen bonding characteristic of the substituent, and length of the n-alkyl chain. To aid in explaining the results, 1) changes in the surface energy component (i.e., non-polar and polar) values that water undergoes during its phase change from liquid to solid that arise from the freezing of impacting supercooled water droplets on the surface depended upon the temperature during accretion were taken into account and 2) the physical properties (i.e., water solubility and melting point) of small compounds analogous to the substituted n-alkyldimethylalkoxysilanes used in this study were compared